We have recently shown that a "cocktail" containing cytokines, neurotrophic factors and extracellular matrix proteins (ECMs) can reliably convert mesencephalic progenitor cells into a culture containing approximately 25% dopamine (DA) neurons. The use of these progenitor cells as a continuous source of DA neurons for transplantation in Parkinson~s disease (PD) would circumvent the ethical concerns and logistical problems that complicate an otherwise straightforward surgical treatment for this disease. However, before these cells can be used, fundamental issues need to be addressed. Two of these form the basis of this proposal. Specific Aim 1 will systematically determine the relative contributions of interleukin - 1alpha (IL-1alpha), leukemia inhibitory factor (LIF), IL-11, glial derived neurotrophic factor (GDNF), mesencephalic membrane fragments and striatal conditioned media to the differentiation and maturation of progenitor cells to the DA neuron phenotype in tissue culture. Tyrosine hydroxylase and DA transporter proteins, the production of DA and the development of axonal varicosities will operationally define the DA phenotype. The expression of nestin, GFAP, and GAL-C which will, respectively, identify the percentage of progenitor cells, astrocytes and oligodendrocytes present in the cultures will also be evaluated. Specific Aim 2 will determine if converted progenitor cells can be grown in rotary cultures and transplanted into the brain of a rat. Rotational behavior, in vivo microdialysis, and immunohistochemical assessment of the same markers used in vitro will be performed in the grafted animals and compared to animals transplanted with 'traditional' fetal nigral grafts. Implementing these specific aims would address the overall issue of whether progenitor cells are a potential source of tissue for neurotransplantations in PD.